1. Field of the Invention
The present invention relates generally to an image forming apparatus that prints an image on a recording medium.
2. Description of the Related Art
A conventional image forming apparatus such as a copying machine, a printer, or a facsimile machine employs an electrophotographic process. A charging device uniformly charges the surface of a photoconductive body. An exposing device such as a laser scanner or an LED head illuminates the charged surface to write an electrostatic latent image on the photoconductive body. A developing device supplies toner to the electrostatic latent image to form a toner image. The toner image is transferred onto a recording medium such as paper or a film directly or indirectly via an intermediate transfer system. The recording medium is then advanced to a fixing device where the toner image is fused to the recording medium.
The image forming apparatus includes a feed roller that feeds sheets of paper from a paper cassette into a transport path, a pair of registry rollers disposed downstream of the feed roller, and a paper sensor disposed downstream of the registry rollers at a widthwise mid point of the transport path. The recording medium is transported on a sheet-by-sheet basis. When continuous printing is performed, a following sheet of two consecutive sheets is fed a predetermined amount of time after the trailing end of a preceding sheet is detected by the sensor.
More than one sheet of recording medium may be on the transfer belt simultaneously in continuous printing. It is desirable that the gap between successive sheets (i.e., interpage gap or interpage distance) is constant. However, the transfer belt may not run at the same speed as the paper transporting mechanism, in which case, the interpage gap may not be always constant. This is particularly true if the recording medium is thick and rigid so that the recording medium is difficult to flex and moves relative to the transfer belt. This causes positional errors of the recording medium and therefore color shift in a printed image.